1. Field of the Invention
This invention relates to computer systems and more particularly to power management of computer systems.
2. Description of the Related Art
Power consumption and associated performance and thermal issues are considerations for every computer system design. Many power saving techniques have been introduced to save power. Power management in older personal computer systems was typically implemented using micro-controllers and/or proprietary use of the system management mode (SMM). Current ×86 based computer systems utilize an industry supported power management approach described in the Advanced Configuration and Power Interface Specification (ACPI). The ACPI specification enables an operating system (OS) controlled power management scheme. As part of that power management approach, ACPI specifies processor and device power states and system sleep states. One such state specified by ACPI is the S3 or suspend to RAM state where the state of the machine is saved to RAM. When in the S3 state, activity on peripheral devices such as a keyboard or mouse causes the device to wake from the S3 state. Accordingly, even though the system is in a low-power state, the system has to provide power to maintain system state in RAM as well as to power sufficient logic to detect peripheral activity and cause the system to wake from the S3 state. Other reduced power states include suspend to disk (STD), in which system context is saved to non volatile memory such as the hard disk and soft off.
It would be desirable to be able to provide a cost effective solution to detect the existence of the S3 state and to provide a mechanism to detect a wake-up event that is cost effective, requires few parts and can be implemented in the motherboard or integrated into the chipset.